The tricky thing is that there can be more than one correct answer -- and unfortunately, sometimes you can choose the "wrong" starting note so that your counter-melody is fine for a few notes, but then there will be no way to continue.

That's part of how counterpoint works, though -- and that's why there's a button to delete notes from your response. It's not an error to remove a note (or even all of them!) if you have gotten yourself into a corner.

Fortunately, as you practice more the whole process gets a lot quicker, and you can scan ahead to see if there will be a tricky part coming up so you can lead into it safely.

I do hope to put the option for hints in future versions, since it'd be nice to click a button and see all possible options for the next note (if there are any!).